In order to minimize the weft thread waste, published European Patent Application 0,240,075 (Moenclaey et al.) discloses a method and an apparatus for carrying out the method, wherein at least two weft thread supply arrangements are used, and at least two weft threads are presented, clamped and fastened, for forming the woven web. The method can essentially be characterized as follows. The free ends of at least first and second weft threads that are to be successively inserted into a loom shed are clampingly held, each respectively in a respective moving clamp on a thread presenting lever arm of a thread presenting and clamping arrangement. At this time, the lever arms are located in a first position A. Next, a weft thread selector selects a single weft thread from the two weft threads, for presentation to an insertion gripper. The corresponding thread presenting lever arm is moved into a second position B and thereby brings the selected weft thread into the path of the insertion gripper, which in turn takes over the selected weft thread. Thereafter, the thread presenting lever arm is moved into a position C, located near the insertion side web edge along the continuation of the line of the beat-up edge of the woven web. After it is inserted into the loom shed and bound-in, the above mentioned weft thread, which remains connected with the thread supply, is held clamped by the corresponding clamp in the position C. Next, the bound-in weft thread is cut from the clamped weft thread that is held ready and connected to the thread supply, by means of a weft thread cutter, between the web edge and the clamp located in position C. After the weft thread has been cut off, the corresponding thread pre senting lever arm is moved back into the position A or is main tained in the position C.
The above described known method, as well as the associated apparatus for carrying out the method as will be described below, suffer the grave disadvantage that the different weft thread types that are to be inserted necessarily respectively have different thread waste end lengths. Namely, since the several thread clamps respectively holding the different weft thread types are arranged laterally adjacent one another spaced from the woven web edge, the amount of thread waste will necessarily differ among the threads held in the different clamps. Thus, while the thread clamp positioned closest to the web edge will realize a relatively small thread waste length, the thread waste lengths of the weft threads held by the remaining thread clamps will be successively comparatively greater. This successive increase of the thread waste length is necessitated by the arrangement of the apparatus, and is a significant disadvantage, making it impossible to truly minimize the total thread waste, and resulting in different amounts of waste from the respective different thread supply spools.
To further describe the above mentioned disadvantage, the prior apparatus according to published European Patent Application 0,240,075 will now be briefly discussed. The known apparatus for presenting and clamping weft threads in a gripper loom essentially comprises a respective thread presenting lever arm with a corresponding thread clamp for each weft thread type that is to be inserted into the loom shed. The thread presenting lever arms are arranged respectively adjacent to one another approximately parallel to the insertion-side web edge. Thereby the clamp of the first thread presenting lever is positioned closest to the web edge in the positions A and C, while the clamp of the last thread presenting lever is positioned farthest away from the web edge. From this arrangement it becomes clear that the free thread length between the fixed position of the thread cutter at the woven web edge and each of the clamps following the first clamp must be regarded as a further disadvantage. Namely, as the thread length between the thread cutter and the respective thread clamp becomes greater, generally the thread tension in the thread, as is necessary for carrying out the cutting, will become smaller. In this regard, the known apparatus cannot ensure that all of the weft threads will be properly cut to form a regular cut edge along the insertion side of the loom shed.
German Patent Laying-Open Document 2,531,954 discloses a controllable weft thread clamping arrangement with a plurality of clamping members, whereby each clamping member is slideably displaceable relative to a reference plane, and whereby further the clamping members are arranged above one another at respective constant uniform spacings. With this known arrangement, respectively one clamping member can be slidingly displaced into the reference plane at a time. This clamping arrangement is provided in combination with generally known controlled weft thread selectors, in other words, each clamping member of the controlled clamping arrangement is correspondingly associated with a respective controlled weft thread selector as required by the functioning of the apparatus.
In this manner, the known arrangement according to German Patent Laying-Open Document 2,531,954 achieves the advantage that the respective weft thread to be inserted into the loom shed can be moved into a first reference plane, where the respective weft thread is taken over by the insertion gripper without problems. On the other hand, the respective clamping member can be moved into a second reference plane, which corresponds to the position of the binding point or binding edge of the woven web. Hereby it is achieved that the weft thread is held by the respective corresponding clamping member of the clamping arrangement while the weft thread is being beat-up against the binding edge of the woven web, and the respective weft thread is held under tension on the insertion side of the loom shed between the web edge and the clamping location. This is advantageous for carrying out the cutting process, which is achieved by the thread cutter arranged between the clamping location and the web edge. However, it is not possible to absolutely minimize the weft thread waste with this arrangement, because the weft threads cannot be directly presented to the insertion gripper.
Furthermore, published European Patent Application 0,644,286 (Stacher et al.) discloses a controllable weft thread clamping arrangement including a plurality of clamping members, of which the structure and function essentially corresponds to that disclosed in the above described German Patent Laying-Open Document 2,531,954. This reference provides no further disclosure or suggestions toward minimizing the weft thread waste.